After Daniel M. Abrams, a researcher from Northwestern University, and a colleague analyzed real world data, they found the cooperation theory is in fact true.

“The more social the animal — where cooperation is highly valued — the more the general population will trend toward one side,” he said. “The most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority.”

The result is that most of us — nine out of 10, to be exact — are same-hand dominant and can thus share common objects like tools without issue.

So why isn’t everyone right-handed?

Abrams says the 10 percent of people who are left-handed prove that humans aren’t always entirely cooperative. Researchers created a new model by which they can even predict how many lefties there will be in any group of humans or animals given data about the degrees of cooperation and competition within the social structure of that group.

In particular, being left-handed in the sports world is a plus, which shores up the idea that being unusual provides an advantage — especially among baseball players, boxers or fencers.